A recirculating grinding installation with a static sifter arranged above the roller press is known from EP 0 650 763 A1, wherein the oversized material from the sifter arrives in the feed shaft of the roller press by means of gravity. The fresh material, together with the slugs from the roller press output, is fed via a conveying mechanism to the static sifter. Furthermore, DE 10 221 739 A1 shows an arrangement in which the roller press is arranged above the static sifter. In this context, the width of the sifter is essentially matched to the width of the grinding rollers, such that the comminuted grinding stock reaches the static sifter with an optimum distribution across the width. However, both variants require a high expenditure in terms of construction and lead to a very great overall height. In particular, arranging the roller press above the static sifter is associated with enormous costs on account of the high weight.
In the interim, it has further been found that the efficiency of the static sifter can be increased if it is made wider and accordingly not as high. According to EP 1 786 573 B1, in that context, a ratio of width to vertical height of the aeration plate of at least 0.45 has been found to be particularly advantageous. However, roller presses are usually only 1.5 to maximum 2 m wide and a significant width increase cannot currently be envisaged. For that reason, very high and narrow static sifters are presently used. If one wished to position a wider and accordingly lower sifter beneath a roller press, it would be necessary to provide means for distributing the roller press output material over the breadth of the sifter. However, such measures require additional overall height.
Moreover, U.S. Pat. No. 1,002,504 A discloses a grinding installation which contains a roller press for comminuting brittle grinding stock with two counter-rotating grinding rollers, and also a static sifter with a sifting stock inlet for grinding stock comminuted in the roller press, with an outlet for oversized material and an outlet for fine material, wherein the outlet for oversized material is connected to the roller press. This grinding installation further contains a conveying mechanism which lifts the output of the roller press to the sifting stock inlet of the static sifter.
Finally, DE 694 21 994 T2 shows a grinding installation with a roller mill and a classifying device of the fluidized bed type. The box-shaped housing of this classifying device is divided, by a porous, inclined separating plate, into an upper fluidized bed chamber and a lower air inlet chamber. The grinding stock to be classified is introduced on one side from above into the fluidized bed chamber, while on the other side the fluidized fine material is removed upward and the oversized material which does not float is withdrawn downward.